See Cluster's comment, but I can add one piece of data: I did a couple measurements of my DSG Hitchhiker (G48) both with, and without, my JCP attached. I pressed the holster down onto my desk and took a measurement at a specific place on the holster. The delta (meaning how much the JCP added) was 0.1".
So, yeah, visually it seems bulky, but with a total weight of mine as made (fabric, velcro, thread, Poly-Fil) of 10 grams, it really squishes down when in use.